Gregg Garfin

Climate Snapshot

An active jet stream ferried several storms into the Southwest in the last 30 days, delivering cool conditions but little precipitation (Figure 1).

With the exodus of monsoon moisture around mid-September, nighttime temperatures nose-dived during these storms, causing early frostnip on some crops across the Southwest.

Although conditions were drier than average across the Southwest in the last month, this time of year is often dry and drought conditions are usually locked in for a few months after the end of the monsoon. The good news is that copious summer rain substantially improved short-term drought across the Southwest. Extreme drought, for example, covered about 22 and 90 percent of Arizona and New Mexico, respectively, on June 18. Currently, those conditions span only about 3 percent of New Mexico; Arizona is free of extreme drought. Similarly, only about 25 and 38 percent of Arizona and New Mexico are classified with severe drought, down from 72 and 98 percent at the onset of the monsoon (Figure 2).

The bad news is the accumulated precipitation deficits over longer timescales. The 12-, 18-, and 24-month standard precipitation index (SPI), which tallies local precipitation anomalies over these intervals, show abnormally dry conditions across many parts of the Southwest. The effects of these protracted dry conditions are most evident in water stored in large reservoirs. Elephant Butte in New Mexico, while experiencing a recent bump of about 72,000 acre-feet, largely from September rains, remains at only 8 percent of capacity. Storage in Lakes Mead and Powell also has dwindled in recent years, with the U.S. Bureau of Reclamation lowering water flows from Lake Powell to Lake Mead beginning on October 1 due to diminished Upper Colorado River Basin (UCRB) streamflow.

This winter brings a drought inflection point. Meager snowfall in the UCRB will cause Lake Mead’s water elevation to approach 1,075 feet above sea level (asl), the trigger elevation for the first tier of Colorado River water shortage (it currently sits at 1,106 feet asl). Large snowpacks can help stave off shortages. Water managers and farmers tied into the Rio Grande also are keenly watching snowpack conditions. With the El Niño-Southern Oscillation in a neutral phase, forecast models are unclear if the headwaters of both the Rio Grande and Colorado River will receive above-average precipitation (Figure 3).

Neutral events, however, often have high month-to-month and seasonal variability.